<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style>
        
    </style>
</head>
<body>
    
</body>
<script>

    var a = 10;
    console.log(a);

    var b;
    console.log(b);

    var c = a;
    console.log(c);

    var d = "true";
    console.log(typeof d);

    var q, w="hello", e, r=30;

    console.log(q); //undefined
    console.log(w); //hello
    console.log(e); //undefined
    console.log(r); //30
    
</script>
</html>